Concrete Block Fill Calculator

Find how much grout is needed to fill concrete block cores, and the bag count and cost.

⏱ Updated: 18 Sep 2026

Calculator

Free concrete block fill calculator: find how much grout is needed to fill CMU block cores, and the bag count and cost.

80 lb Bags
Grout Volume (ft³)
Estimated Material Cost
$

Default core volume (0.28 ft³/block) reflects the typical ~45% void fraction of a standard two-core 8x8x16 in. CMU — check your block manufacturer's spec if precision matters. Bag count assumes a standard coarse grout yield of 0.45 ft³ per 80 lb bag.

Enter the number of blocks and how much of each core to fill to calculate grout volume, bags, and cost.

Grouting CMU cores — filling the hollow centers with concrete grout, usually around vertical rebar — is a different material take-off than laying the block itself, and this tool covers that second step on its own.

How to Use the Concrete Block Fill Calculator

Enter the number of blocks to fill, what share of their cores get grout (100% for solid grouting, lower for spot-filling around rebar cells only), and the core volume of your specific block. Bag count and cost update as you type.

Core volume is the field most worth double-checking. A standard two-core 8x8x16 in. CMU has roughly 45% of its gross volume hollow — call it about 0.28 cu ft of open core per block — but manufacturers vary the web thickness enough that this isn't a fixed physical constant the way the block's outer dimensions are. Treat the default as a starting estimate, not a spec.

grout volume = number of blocks × core volume per block × (fill % ÷ 100)
80 lb bags = grout volume ÷ 0.45 ft³

Partial fill is common in practice — many walls only grout the cells that carry vertical rebar, spaced every 32 or 48 in., rather than every core in the wall. Lower the fill percentage to match whatever cell spacing your plans actually call for instead of assuming a fully solid wall.